First, make sure you're downloading the right package
(one intended for your version of perl),
and then simply download it
(ex: WWW-Curl.tar.gz).
Then, uncompress it so now you have a blib directory in your current
working directory, and then execute

perl -MExtUtils::Install -e install_default WWW/Curl

and voila. It's what PPM basically does.

BE AWARE that the .ppd file may contain instructions
to download extra files needed for install, which
are not packaged with the tarball (like
libcurl.dll, libeay32.dll, ssleay32.dll).
You'll have to examine the .ppd file to make sure.